I think I have worked out why I'm so tired.

Thanks guys for all the replies.  I am currently using a B12 Sublingual spray and my bloods actually show my B12 as fantastic but my iron is low.  So I'm really hoping that these Tendor Iron capsules don't take too long to kick in.  Fingers crossed as i'm trying to avoid having an iron infusion by IV as the doctor has suggested. :(